In my recent patent as noted above, there is disclosed a building structure including and outer walls with air passages therebetween, sized gravel both in subterranean pits and in a layer beneath the floor of the structure, and fans and ducts for circulating the air through the wall passages to collect solar heat, through the gravel to store or recover heat, and through the interior of the building to heat or cool same.
The storage of heat in rocks in solar energy systems is known per se, though rock is more commonly used as an insulator around a tank where a fluid heat transfer medium (e.g., water or glycol) is stored.
Recent substantial development of solar energy systems, spurred by tax benefits and grant programs, has concentrated on domestic hot water heating. The heat transfer fluid must be a glycol, silicone or other anti-freeze type solution, and the danger always exists (e.g., of a leak) that will result in contamination of the water supply or, in systems where the water is held at a higher pressure than the fluid, dilution of the fluid. Such systems are also subject to catastrophic failure during a day-time summer power failure, since temperatures in the solar collectors will quickly rise to over 200.degree. F. in the absence of circulation of the fluid. In contrast to the foregoing, the emphasis in my patent and in the present invention is on space heating, with air as both the heat transfer fluid and the heating medium. While the heat capacity of ambient air is of course much less than other fluids, it is free, it is non-contaminating and, most surprisingly, in accordance with the present invention as described hereinbelow, the energy costs in pumping air are very small in comparison with the value of heat saved.